Stereoscopic image output device and stereoscopic image output method

ABSTRACT

Provided is a stereoscopic image output device including: an image acquisition unit which acquires a left-eye image and a right-eye image which form a stereoscopic image; a display unit which alternately displays the left-eye image and the right-eye image acquired by the image acquisition unit; a safety determination unit which determines whether the stereoscopic image is a safe image by comparing a normal distribution curve of disparities between corresponding points in the left-eye image and the right-eye image and a safe range of disparity indicating a range of disparity in which the stereoscopic image is recognized as a safe image for a viewer; and a notification unit which notifies the viewer that the stereoscopic image is not a safe image when the safety determination unit determines that the stereoscopic image is not a safe image.

TECHNICAL FIELD

The present invention relates to stereoscopic image output devices andstereoscopic image output methods, and, more particularly, to astereoscopic image output device and a stereoscopic image output methodwhich consider safety for a viewer.

BACKGROUND ART

Conventionally, image display devices are known which select, from amonga plurality of captured images, a pair of images for use as a left-eyeimage and a right-eye image for stereoscopic viewing, and display astereoscopic image using the pair of images (for example, see PTL 1).

Such image display devices present to a user a plurality of pairs ofimages the similarity of which is within a predetermined threshold, anddisplay a pair of images selected by the user from among the presentedpairs of images as a left-eye image and a right-eye image. This allowsthe user to view the selected images as a stereoscopic image.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No.2004-104330

SUMMARY OF INVENTION Technical Problem

The stereoscopic image created by the image display devices describedabove, however, may include a left-eye image and a right-eye image thedisparity therebetween is significantly large. In other words, when theuser views such images, the user's health may be adversely affected.

Thus, the present invention is made in light of the above problems andhas an object to provide a stereoscopic image output device and astereoscopic image output method which can properly determine the safetyof a stereoscopic image and notify the safety to the user whendisplaying a stereoscopic image.

Solution to Problem

To solve the above problem, a stereoscopic image output device accordingto one aspect of the present invention is a stereoscopic image outputdevice including: an image acquisition unit configured to acquire aleft-eye image and a right-eye image which form a stereoscopic image; anoutput unit configured to output the left-eye image and the right-eyeimage acquired by the image acquisition unit; a safety determinationunit configured to determine whether the stereoscopic image is a safeimage by comparing a normal distribution curve obtained from disparitiesbetween corresponding points in the left-eye image and the right-eyeimage and a safe range of disparity indicating a range of disparity inwhich the stereoscopic image is recognized as a safe image for a viewer;and a notification unit configured to notify the viewer that thestereoscopic image is not a safe image when the safety determinationunit determines that the stereoscopic image is not a safe image.

According to the above configuration, a safe stereoscopic image can beoutputted by correctly determining and notifying a user of the safety ofthe stereoscopic image.

Moreover, the safety determination unit may extract, from the left-eyeimage and the right-eye image, a plurality of feature points forspecifying a shape of a subject included in the stereoscopic image,calculate disparities between the feature points corresponding to eachother in the left-eye image and the right-eye image, and approximate afrequency distribution of the calculated disparities, to calculate thenormal distribution curve.

Moreover, the safety determination unit may determine that thestereoscopic image is a safe image when a percentage of an area of aregion included in the safe range of disparity over an area of a regionenclosed by the normal distribution curve is greater than or equal to apredetermined threshold.

Moreover, the output unit may be a display unit configured toalternately display the left-eye image and the right-eye image, and whenthe safety determination unit determines that the stereoscopic image isnot a safe image, the notification unit may show, on the display unit,that the stereoscopic image is not a safe image.

Moreover, the display unit may altern ately display the left-eye imageand the right-eye image only when the safety determination unitdetermines that the stereoscopic image is a safe image.

Moreover, the stereoscopic image output device may further include astereoscopic image generation unit configured to acquire a first imageand a second image obtained by taking images of a subject from differentpositions, and rotate or move the second image so that disparitiesbetween corresponding points in the first image and the second image areminimized in a vertical direction of the first image and the secondimage, to generate a third image, wherein the image acquisition unit mayacquire one of the first image and the third image as the left-eyeimage, and the other as the right-eye image.

Moreover, the image acquisition unit may acquire a plurality of theleft-eye images and a plurality of the right-eye images which form astereoscopic video in a playback order of the stereoscopic video.

Moreover, the safe range of disparity may be a range of disparitydetermined by a biomedical safety guideline.

Moreover, a stereoscopic image output method according to one aspect ofthe present invention is a stereoscopic image output method including:(a) acquiring a left-eye image and a right-eye image which form astereoscopic image; (b) alternately outputting the left-eye image andthe right-eye image acquired in step (a); (c) determining whether thestereoscopic image is a safe image by comparing a normal distributioncurve of disparities between corresponding points in the left-eye imageand the right-eye image and a safe range of disparity indicating a rangeof disparity in which the stereoscopic image is recognized as a safeimage for the viewer; and (d) notifying the viewer that the stereoscopicimage is not a safe image when it is determined that the stereoscopicimage is not a safe image.

Advantageous Effects of Invention

According to a stereoscopic image output device and the stereoscopicimage output method of the present invention, the display of a safestereoscopic image is possible by correctly determining, using a normaldistribution of disparities, the safety of the stereoscopic image andnotifying the determination result to a user.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a stereoscopicimage output device according to an embodiment of the present invention.

FIG. 2 is an example display of a message indicating that a stereoscopicimage is not a safe image.

FIG. 3 is a flowchart illustrating operation of the stereoscopic imageoutput device according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating a method for generating a stereoscopicimage by a stereoscopic image generation unit.

FIG. 5 is a flowchart illustrating generation of a stereoscopic image bythe stereoscopic image generation unit.

FIG. 6 is a flowchart illustrating a safety determination process of asafety determination unit.

FIG. 7 is a diagram illustrating signs of disparity.

FIG. 8 is a diagram showing an example where incorrect feature pointsare associated with each other.

FIG. 9 is a diagram showing another example where incorrect featurepoints are associated with each other.

FIG. 10 is a diagram showing an example distribution of disparitieswhich is determined to be safe by the safety determination unit.

FIG. 11 is a diagram showing an example distribution of disparitieswhich is determined to be unsafe by the safety determination unit.

FIG. 12 is a diagram showing an application of the stereoscopic imageoutput device according to the embodiment of the present invention.

FIG. 13 is a diagram showing another application of the stereoscopicimage output device according to the embodiment of the presentinvention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withaccompanying drawings.

It should be noted that the embodiments described below are each merelya preferred illustration of the present invention. Values, shapes,materials, components, disposition or a form of connection between thecomponents, steps, and the order of the steps are merely illustrative,and are not intended to limit the present invention. Moreover, amongcomponents of the below non-limiting embodiments, components not setforth in the independent claims indicating the top level concept of thepresent disclosure will be described as optional components forpreferable embodiments.

First, the configuration of a stereoscopic image output device will bedescribed.

FIG. 1 is a block diagram showing the configuration of a stereoscopicimage output device according to an embodiment of the present invention.

As shown in FIG. 1, a stereoscopic image output device 100 includes astereoscopic image generation unit 101, an image acquisition unit 102, asafety determination unit 103, a notification unit 104, a display unit106 (an output unit), and an input unit 107.

It should be noted that the stereoscopic image output device 100 mayinclude, while not shown, components such as a reception unit whichreceives broadcast signals, a communication unit which establishes aconnection to a network, a physical medium attachment for connection toa recording medium, and a sound output unit for outputting soundsignals. These components, however, are not directly related to thepresent invention. Thus, the description will be omitted in the presentembodiment.

The stereoscopic image generation unit 101 generates a left-eye imageand a right-eye image which form a stereoscopic image, and outputs theleft-eye image and the right-eye image to the image acquisition unit102. The left-eye image is an image which forms a stereoscopic image andto be shown to the left eye of a viewer. The right-eye image is an imagewhich forms a stereoscopic image and to be shown to the right eye of theviewer. The stereoscopic image generation unit 101, for example, takesan image by using an imaging device (not shown), and generates astereoscopic image (the left-eye image and the right-eye image). Inother words, the stereoscopic image output device 100 is applicable todigital still cameras (DSC) and the like.

It should be noted that the stereoscopic image generation unit 101 mayacquire two-dimensional images from broadcast waves or a recordingmedium, and generate a stereoscopic image from the acquiredtwo-dimensional images.

The image acquisition unit 102 acquires a left-eye image and a right-eyeimage which form a stereoscopic image which allows a user tostereoscopically view a subject, and outputs the left-eye image and theright-eye image to the safety determination unit 103 and the displayunit 106 (output unit).

Specifically, the image acquisition unit 102 acquires the left-eye imageand the right-eye image generated by the stereoscopic image generationunit 101.

It should be noted that the stereoscopic image generation unit 101 maybe omitted and the image acquisition unit 102 may directly acquire theleft-eye image and the right-eye image.

In this case, the image acquisition unit 102 may acquire images throughbroadcast waves or a communication network. Specific examples of thebroadcast waves are not particularly limited. For example, the imageacquisition unit 102 acquires images from analog broadcasting,terrestrial digital broadcasting, broadcast satellite (BS) broadcasting,and communication satellite (CS).

In other words, the stereoscopic image output device 100 is applicableto television sets and the like.

Also, the image acquisition unit 102 may retrieve images from arecording medium. Specific examples of the recording medium are notparticularly limited. For example, the image acquisition unit 102acquires images from digital versatile disc (DVD), blu-ray disc (BD),secure digital (SD) cards, or the like.

In other words, the stereoscopic image output device 100 is applicableto Blu-Ray recorders and the like.

The safety determination unit 103 determines whether a stereoscopicimage acquired by the image acquisition unit 102 is a safe image.Specifically, the safety determination unit 103 compares a safe range ofdisparity and a normal distribution curve of disparities betweencorresponding points in the left-eye image and the right-eye image todetermine whether the stereoscopic image is a safe image. In the presentembodiment, it is determined whether a stereoscopic image is a safeimage, based on the area of a region enclosed by the safe range ofdisparity and the normal distribution curve of disparities. The saferange of disparity in the present embodiment is a range of disparity setby a biomedical safety guideline.

The above safe range of disparity is quantification of the biomedicalsafety guideline defined by Japan Electronics and Information TechnologyIndustries Association. Specifically, the safe range of disparityindicates a range of disparity that is recognized biomedically safe, andis quantification according to the resolution, the number of inches, anda viewing distance of the display unit 106 to a user.

When the safety determination unit 103 determines that the stereoscopicimage is not a safe image, the notification unit 104 notifies the viewerthat the stereoscopic image is not a safe image. In the presentembodiment, the notification unit 104 displays on the display unit 106 amessage (image) indicating that the stereoscopic image is not a safeimage.

FIG. 2 shows an example display of such a message indicating that astereoscopic image is not a safe image.

As shown in FIG. 2, in the present embodiment, the notification unit 104displays, on the display unit 106, messages indicating that thestereoscopic image is not a safe image and asking the viewer forinstructions as to whether to permit to display the stereoscopic image.This allows the viewer to select whether to display the stereoscopicimage by inputting the instructions via the input unit 107 describedbelow.

It should be noted that the notification from the notification unit 104that the stereoscopic image is not a safe image is not limited thereto.For example, the notification unit 104 may so notify the user byoutputting a sound via a speaker not shown, indicating that thestereoscopic image is not a safe image.

The display unit 106 displays the left-eye image and the right-eyeimage. The display unit 106 according to the present embodiment is adisplay which displays a stereoscopic image by alternately displayingthe left-eye image and the right-eye image in a fixed cycle. Examples ofthe display unit 106 include a liquid crystal display, a plasma display,and an organic electro luminescence (EL) display.

In the present embodiment, the viewer views the display, wearingeyeglasses for stereoscopic image viewing. The eyeglasses forstereoscopic image viewing open and close liquid crystal shutters ofleft and right lens, in synchronization with a time at which the displayunit 106 displays the left-eye image and the right-eye image, therebyallowing the viewer to view a stereoscopic image. In this case, thedisplay unit 106 alternately outputs the left-eye image and theright-eye image, according to the display timing, and, at the same time,outputs, to the eyeglasses for stereoscopic image viewing, instructionsto open and close the liquid crystal shutters in accordance with thetime at which the left-eye image and the right-eye image are outputted.

The display unit 106 may be, for example, a display device which canperform stereoscopic display, without requiring the eyeglasses forstereoscopic image viewing, such as a liquid crystal display which has alenticular lens on a display surface.

It should be noted that the display unit 106 is not necessary. An outputunit which outputs a stereoscopic image may be provided instead of thedisplay unit 106, and the output unit may output a stereoscopic image toa display device which is different from the stereoscopic image outputdevice 100.

The input unit 107 is a user interface which receives input of variousinstructions (requests) from a viewer. The input unit 107 according tothe present embodiment is a remote controller. It should be noted thatthe input unit 107 may be a graphic user interface (GUI) or the likewhich accepts operation of a touch panel overlaid on a display screen ofthe display unit 106.

Next, the overall operation of the stereoscopic image output device 100will be described.

FIG. 3 is a flowchart illustrating the overall operation of thestereoscopic image output device 100 according to the embodiment of thepresent invention.

First, the stereoscopic image generation unit 101 generates astereoscopic image (S301). Details of a method for generating astereoscopic image according to the present embodiment will be describedbelow.

Next, the image acquisition unit 102 acquires the left-eye image and theright-eye image generated by the stereoscopic image generation unit 101.

Next, the safety determination unit 103 determines whether thestereoscopic image (the left-eye image and the right-eye image) acquiredby the image acquisition unit is safe for a viewer (S303). Specifically,first, the safety determination unit 103 calculates, for pairs ofcorresponding points, disparities between a plurality of points in oneof the left-eye image and the right-eye image and a correspondingplurality of points in the other. In the present embodiment, inparticular, the safety determination unit 103 calculates a disparity foreach pair of feature points for specifying a shape of a subject includedin the stereoscopic image.

Next, the safety determination unit 103 determines whether thestereoscopic image is a safe image by comparing a normal distributioncurve, in which the distribution of the calculated plurality ofdisparities is approximated, and the safe range of disparity whichindicates a range of disparity in which the stereoscopic image isrecognized as a safe image for the viewer. Detail of a method fordetermining the safety of an image by the safety determination unit 103will be described.

When the safety determination unit 103 determines that the stereoscopicimage is a safe image (Yes in S303), the display unit 106 alternatelydisplays the left-eye image and the right-eye image on the displayscreen (S304).

When the safety determination unit 103 determines that the stereoscopicimage is not a safe image (No in S303), first, the notification unit 104displays a message indicating that the stereoscopic image is unsafe asshown in FIG. 2, and asks the viewer for instructions whether to permitdisplay of the stereoscopic image (S305).

The viewer inputs, through the input unit 107, instructions to permit orforbid the display of an unsafe image notified by the notification unit104.

When the viewer permits the display of the stereoscopic image,specifically, when the viewer selects “Yes” using a remote controller(Yes in S305) in a state where the message of FIG. 2 is being displayed,the display unit 106 displays the stereoscopic image (S304).

On the other hand, when the viewer permits the display of thestereoscopic image, that is, when the viewer selects “No” to the messageshown in FIG. 2 (No in 305), the display unit 106 ends the processing,without displaying the stereoscopic image.

It should be noted that the notification unit 104 may not ask the viewerfor the instructions whether to permit the display of the stereoscopicimage. In such a case, when the safety determination unit 103 determinesthat the stereoscopic image is not a safe image, the display unit 106does not display the stereoscopic image. In other words, the displayunit 106 alternately displays the left-eye image and the right-eye imageonly when the safety determination unit 103 determines that thestereoscopic image is a safe image.

Next, details of the method for generating a stereoscopic image by thestereoscopic image generation unit 101 will be described.

FIG. 4 is a diagram illustrating the method for generating astereoscopic image by the stereoscopic image generation unit 101.

FIG. 5 is a flowchart illustrating generation of a stereoscopic image bythe stereoscopic image generation unit 101. FIG. 5 is a flowchartillustrating details of step S301 of the flowchart of FIG. 3.

First, as shown in (a) of FIG. 4, the stereoscopic image generation unit101 acquires an image (S501 of FIG. 5). The stereoscopic imagegeneration unit 101 according to the present embodiment acquires twoimages, a first image 120 and a second image 130, by way of example. Thefirst image 120 and the second image 130 are images obtained by takingimages of the same subject from different viewpoints in the horizontaldirection, and the images have a disparity therebetween in thehorizontal direction of the images. Also, unintended shit is present inthe different viewpoints in the vertical direction, due to a tilt of animaging device used for taking the images of the subject. In otherwords, the first image 120 and the second image 130 have a disparitytherebetween in the vertical direction of the images as well. Forgeneration of a stereoscopic image by using the first image 120 and thesecond image 130, the disparity between the images in the verticaldirection is not necessary. Thus, a process is performed as below inwhich the disparity between the first image 120 and the second image 130in the vertical direction is cancelled while keeping the disparity inthe horizontal direction.

First, as shown in (b) of FIG. 4, the stereoscopic image generation unit101 detects edges which are outlines of the subject in the first image120 and the second image 130 (S502 of FIG. 5). For example, a Laplacianfilter is used to detect the edges of the subject. The Laplacian filteris a filter which extracts, for each pixel of an image, a portion inwhich an amount of change in brightness is extreme. In other words, oneof corresponding portions in the first image 120 and the second image130, in which changes in brightness is greater than the other isdetected as the edge. It should be noted that a portion in which changesin hue is greater than the other may be detected as the edge.

Next, as shown in (c) of FIG. 4, the stereoscopic image generation unit101 extracts a plurality of feature points in the first image 120 and aplurality of feature points in the second image 130 (S503 of FIG. 5).

Specifically, first, the stereoscopic image generation unit 101 detectsa plurality of feature points on the edges of the subject in the firstimage 120 and the second image 130.

In the example shown in (c) of FIG. 4, the stereoscopic image generationunit 101 extracts feature points 140 a and 140 b in the first image 120,and extracts feature points 140 a′ and 140 b′ in the second image 130.The number of feature points actually extracted is determined in view ofbalance between load of the processing for extracting feature points andaccuracy of an image to be generated.

Subsequently, the stereoscopic image generation unit 101 calculates thebrightness vector of each feature point. The brightness vector is avector indicating a direction in which the brightness changes and amagnitude of changes in the brightness. The brightness vector isobtained from a difference of the brightness of a pixel at a featurepoint from the brightness of pixels around the feature point.

In the example shown in (c) of FIG. 4, the stereoscopic image generationunit 101 calculates a brightness vector 150 a at the feature point 140 aand a brightness vector 150 b at the feature point 140 b in the firstimage 120. Likewise, the stereoscopic image generation unit 101calculates a brightness vector 150 a′ at the feature point 140 a′ and abrightness vector 150 b′ at the feature point 140 b′ in the second image130.

Subsequently, the stereoscopic image generation unit 101 associatesfeature points included in the first image 120 and feature pointsincluded in the second image 130. Specifically, the brightness vector ateach feature point included in the first image 120 and the brightnessvector at each feature point included in the second image 130 arecompared to obtain correlation between the brightness vectors at all thefeature points included in the first image 120 and the second image 130.Based on the obtained correlation between the brightness vectors at allthe feature points, feature points having a similar brightness vectorare associated with each other.

In the example shown in (c) of FIG. 4, the brightness vector 150 a andthe brightness vector 150 a′ are in close correlation. Thus, thestereoscopic image generation unit 101 associates the feature point 140a and the feature point 140 a′. Likewise, the brightness vector 150 band the brightness vector 150 b′ are in close correlation. Thus, thestereoscopic image generation unit 101 associates the feature point 140b and the feature point 140 b′.

Next, as shown in (d) of FIG. 4, the stereoscopic image generation unit101 rotates or moves the second image 130 so that the disparities, inthe vertical direction, between corresponding feature points in thefirst image 120 and the second image 130 are minimized, to generate athird image (S504 of FIG. 5).

The third image is, specifically, as shown in (d) of FIG. 4, obtained bycorrecting (rotating or moving) the second image so that locations ofthe corresponding feature points in the vertical direction of the imageare the same. This can generate the first image and the third image inwhich the disparity therebetween remains only in the horizontaldirection.

Last, the stereoscopic image generation unit 101 outputs one of thefirst image 120 and the third image as the left-eye image to the imageacquisition unit 102, and outputs the other as the right-eye image tothe image acquisition unit 102. Whether the first image 120 or the thirdimage is to be used as the left-eye image is determined based on theorientation of the display between the first image 120 and the thirdimage in the horizontal direction.

In the example shown in (d) of FIG. 4, when the subject is displayedprojecting from the display screen of the display unit 106 toward theviewer, the first image 120 is an image from a viewpoint located to theright of the third image. Thus, the stereoscopic image generation unit101 outputs the first image 120 as the right-eye image and outputs thethird image as the left-eye image.

In contrast, when the subject is displayed receding into the displayscreen of the display unit 106 from the viewer, the stereoscopic imagegeneration unit 101 outputs the first image 120 as the left-eye imageand outputs the third image as the right-eye image.

It should be noted that due to the correction on the second image 130, aregion may occur in which no image data is present in the periphery ofthe third image. In such a case, the peripheries of the first image 120and the third image may be trimmed to remove the regions in which noimage data is present in the peripheries. Alternatively, image data ofthe region in which no image data of the third image is present may beinterpolated using color heuristic included in the image, image data ofthe first image 120 or the like.

Since the association of feature points in step S503 is based on thecorrelation in brightness vector, feature points that are essentiallynot corresponding to each other may be associated due to a fact that thebrightness vectors thereof are similar by chance. Thus, in fact, thestereoscopic image generation unit 101 corrects the images so that thecorresponding feature points are located in a range formed of apredetermined number of pixels in the vertical direction of the images.This allows the stereoscopic image generation unit 101 to reduce thedisparity in the vertical direction of the images.

The details of the method for generating a stereoscopic image by thestereoscopic image generation unit 101 have been described above.However, the method for generating a stereoscopic image is not limitedto the above method.

For example, depth information indicating the depths of a subject inacquired two images may be obtained and an image may be generated whichhas a disparity with one of the acquired images in the horizontaldirection.

Alternatively, it is feasible to generate the left-eye image and theright-eye image even if the stereoscopic image generation unit 101acquires one image. In such a case, for example, the stereoscopic imagegeneration unit 101 may generate an image which has a disparity with oneof the acquired images in the horizontal direction, using colorheuristic included in the image or the like.

Next, details of a method for determining the safety of the stereoscopicimage by the safety determination unit 103 will be described.

FIG. 6 is a flowchart illustrating a safety determination process of thesafety determination unit 103. FIG. 6 is a flowchart furtherillustrating step S303 of the flowchart shown in FIG. 3.

First, the safety determination unit 103 extracts corresponding featurepoints in a left-eye video and a right-eye video which are acquired bythe image acquisition unit 102 (S601 of FIG. 6). In the presentembodiment, the data of the corresponding feature points calculated bythe method described with reference to FIG. 4 and FIG. 5 by thestereoscopic image generation unit 101 may be stored and used as it is.

If the stereoscopic image output device 100 does not include thestereoscopic image generation unit 101, the safety determination unit103 extracts corresponding feature points in the left-eye video and theright-eye video by a method corresponding to steps S502 and S503 of FIG.5.

Next, the safety determination unit 103 calculates a disparity for eachof a pair of corresponding feature points (S602 of FIG. 6). In thepresent embodiment, the disparity between the pair of the correspondingfeature points is represented by the number of pixels on the displayscreen. Also in the present embodiment, the disparity is represented inamount having a sign. Specifically, when the subject is displayedreceding into the display screen from the viewer, the disparity isrepresented in an amount having minus sign. In contrast, when thesubject is displayed projecting from the display screen toward theviewer, the disparity is represented in an amount having plus sign.

FIG. 7 is a diagram illustrating signs of disparity.

Part (a) of FIG. 7 is a top view where the subject is displayed recedinginto the display screen of the display unit 106 from the viewer. Asshown in (a) of FIG. 7, a feature point 140 e in the left-eye image islocated to the left of a corresponding feature point 140 e′ in theright-eye image in the horizontal direction of the images. In such acase, the disparity of the stereoscopic image calculated by the safetydetermination unit 103 is the disparity that has minus sign.

Part (b) of FIG. 7 is a top view illustrating a disparity where thesubject is displayed projecting from the display screen of the displayunit 106 toward the viewer. As shown in (b) of FIG. 7, a feature point140 f in the left-eye image is located to the right of a correspondingfeature point 140 f′ in the right-eye image in the horizontal directionof the images. In such a case, the disparity of the stereoscopic imagecalculated by the safety determination unit 103 is the disparity thathas plus sign.

It should be noted that the disparity calculated as the amount having asign as described above may include a disparity greater or smaller thanan actual disparity. This is because there may be an error atassociation of the feature points in, for example, an image in which aplurality of objects having a similar shape are present, or an imagewhich includes a large number of regions having uniform brightness,since the feature points are associated with each other based on thecorrelation (similarity) in the brightness vector at the feature points.

FIG. 8 and FIG. 9 are diagrams each showing an example where incorrectfeature points are associated with each other.

FIG. 8 shows an example where images of two vehicles having a same modelin line are taken in a left-eye image 160 and a right-eye image 170.

In FIG. 8, a feature point 140 c′ in the left-eye image 160 correspondsto a feature point 140 c in the right-eye image 170. The feature point140 c′ and the feature point 140 c are points on left edges of a vehiclelocated on the right side of the images. In the case of FIG. 8, however,the brightness vector at a point on the left edge of the vehicle locatedto the right side of the right-eye image 170 may resemble the brightnessvector at a point on the left edge of the vehicle located to the leftside of the left-eye image 160. In other words, the feature point 140 cin the right-eye image 170 may incorrectly be associated with thefeature point 140 c″ in the left-eye image 160.

In this case, in the example of FIG. 8, despite a correct amount ofdisparity at the feature point 140 c in the right-eye image 170 is adisparity A, an incorrect disparity A′ is calculated.

FIG. 9 shows an example where there are a large number of regions whichhave uniform brightness in the left-eye image 160 and the right-eyeimage 170. Arrow shapes shown in the left-eye image 160 and theright-eye image 170 of FIG. 9 each have a uniform brightness (color),and the brightness around the arrow shape is also uniform. Thus, manybrightness vectors at points on the edge of the arrow shape are similar.Thus, it is likely that incorrect feature points are associated witheach other.

For example, a feature point 140 d′ in the right-eye image 170corresponds to a feature point 140 d in the left-eye image 160 in FIG.9. However, the feature point 140 d may incorrectly be associated withthe feature point 140 d″ the brightness vector at which resembles thatof the feature point 140 d′ in the left-eye image 160.

In this case, in the example of FIG. 9, despite a correct disparity atthe feature point 140 d in the left-eye image 160 is a disparity B, anincorrect disparity B′ is calculated.

While FIG. 8 and FIG. 9 show the cases where the disparity isincorrectly calculated a large value, there is, of course, a case wherethe disparity is incorrectly calculated a small value.

As described above, for association of feature points using brightnessvectors, the disparity is incorrectly calculated in many cases, and itis very difficult to prevent this altogether.

Thus, in a method where it is simply determined that a stereoscopicimage is unsafe because the number of pairs of feature points thedisparities of which exceed the safe range of disparity is greater thanor equal to a predetermined threshold, a stereoscopic image which is infact safe may be determined to be an unsafe stereoscopic image becauseof the disparities between incorrectly associated feature points.

Thus, the present invention compares the normal distribution curve ofdisparities and the safe range of disparity, rather than counting thenumber of disparities off the safe range of disparity, to correctlydetermine the safety of the stereoscopic image.

First, the safety determination unit 103 obtains an average and varianceof disparities calculated for pairs of corresponding feature points togenerate a normal distribution curve of disparities represented by aprobability density function (S603 of FIG. 6). The probability densityfunction for a disparity x is obtained by the following mathematicalequation where p represents the average of disparities, and a representsstandard deviation.

$\begin{matrix}{\left\lbrack {{Eq}.\mspace{14mu} 1} \right\rbrack \mspace{619mu}} & \; \\{{f(x)} = {\frac{1}{\sqrt{2\pi \; \sigma^{2}}}\exp \left\{ {- \frac{\left( {x - \mu} \right)^{2}}{2\sigma^{2}}} \right\}}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$

Next, the safety determination unit 103 compares the generated normaldistribution curve and the safe range of disparity to determine whetherthe stereoscopic image is a safe image (S604 of FIG. 6).

First, the safe range of disparity will be described. In the presentembodiment, the safe range of disparity is determined by an upper limitand a lower limit of the disparity which are defined by the biomedicalsafety guideline, and is represented by the number of pixels.

The range of the disparity defined by the biomedical safety guidelinewill be described again with reference to FIG. 7.

As shown in (a) of FIG. 7, when the subject is displayed receding intothe display screen from the viewer, the limit of the safe range ofdisparity defined by the biomedical safety guideline is defined within 5cm on the display screen, on which the stereoscopic image is displayed,in the horizontal direction. An amount of the disparity in this case hasminus sign.

Thus, the lower limit of the safe range of disparity is an amount whichrepresents a disparity C corresponding to 5 cm on the display screen inthe horizontal direction by the number of pixels having minus sign addedthereto. The lower limit of the safe range of disparity is,specifically, obtained based on the size of the display screen and theresolution of the display screen.

On the other hand, when subject is displayed projecting from the displayscreen toward the viewer as shown in (b) of FIG. 7, the limit of thesafe range of disparity defined by the biomedical safety guideline isobtained by an angle of convergence represented by an angle θ shown in(b) of FIG. 7. Specifically, the limit of the safe disparity is adisparity on the display screen where the angle of convergence is within1 degree. The disparity in this case is an amount which has plus sign asdescribed above.

Thus, in the present embodiment, the upper limit of the safe range ofdisparity is an amount representing a disparity D corresponding to theangle of convergence within 1 degree on the display screen by the numberof pixels and adding the plus sign to the disparity D. The upper limitof the safe range of disparity is, specifically, obtained based on thesize of the display screen, the resolution of the display screen, and aviewing position of the viewer.

It should be noted that the safe range of disparity is not limited to bedefined by the biomedical safety guideline.

For example, the safe range of disparity may be set to a range disparitynarrower than the range of disparity defined by the biomedical safetyguideline.

FIG. 10 and FIG. 11 are diagrams each illustrating safety determinationby the safety determination unit 103.

In FIG. 10 and FIG. 11, the normal distribution curve obtained from thedisparities, a histogram indicating an actual distribution of thedisparities, and the safe range of disparity defined by the biomedicalsafety guideline are shown. The disparity (the number of pixels) isindicated on the horizontal axes in FIG. 10 and FIG. 11, the number offeature points (frequency) is indicated on the vertical axis. The leftend of the safe range of disparity represents the lower limit describedabove, and the right end of the safe range of disparity represents theupper limit.

FIG. 10 is a diagram showing an example distribution of the disparitiesdetermined to be safe by the safety determination unit 103.

In the present embodiment, the safety determination unit 103 determinesthat the stereoscopic image is a safe image when a percentage of thearea of a region included in the safe range of disparity over the areaof the region enclosed by the normal distribution curve is greater thana predetermined threshold (for example, 90% or above).

The region included in the safe range of disparity in the regionenclosed by the normal distribution curve is a region indicated byhatched lines in FIG. 10. The safety determination unit 103 determinesthat the stereoscopic image is a safe image when the percentage of thearea of the region included in the safe range of disparity over the areaof the region enclosed by the normal distribution curve is greater thanor equal to a predetermined percentage.

In FIG. 10, comparing the histogram and the safe range of disparity,while there are pairs of feature points which have the disparitytherebetween off the safe range of disparity, the area of the regionincluded in the safe range of disparity in the area of the regionenclosed by the normal distribution curve is greater than or equal to apredetermined percentage. Thus, the stereoscopic image which has suchdistribution of disparities is determined to be safe.

On the other hand, FIG. 11 is a diagram showing an example distributionof the disparities determined to be unsafe by the safety determinationunit 103.

In FIG. 10, comparing the histogram and the safe range of disparity,there is no pair of feature points that have the disparity therebetweenoff the safe range of disparity. The stereoscopic image having adistribution of disparities as shown in FIG. 11, however, has largevariations in disparity, and a percentage of the area of the region,indicated by hatched lines in FIG. 11, included in the safe range ofdisparity over the area of the region enclosed by the normaldistribution curve is less than the predetermined percentage. Thus, thestereoscopic image which has such distribution of disparities isdetermined to be unsafe.

Typically, the disparities of the stereoscopic image vary to someextent. However, if the disparities vary to a large extent as in FIG.11, which may cause adversely effect to the viewer such as image-inducedsickness. Also, in the example of FIG. 11, while there is no disparityoff the safe range of disparity, if the disparities vary to a largeextent, a pair of feature points incorrectly associated with each otheras described above may, by chance, have a disparity within the saferange of disparity.

Thus, it is reasonable that the safety determination unit 103 determinesthe stereoscopic image, in which the disparities vary to a large extent,as an unsafe stereoscopic image.

In this manner, the safety determination unit 103 determines the safetyof the stereoscopic image by the normal distribution curve ofdisparities, thereby accurately determining the safety of thestereoscopic image.

It should be noted that the method for determining the safety bycomparison of the normal distribution curve and the safe range ofdisparity is not limited to the above. For example, the safetydetermination unit 103 may determine that a stereoscopic image is a safeimage when an entire region determined by the normal distribution curveof disparities in the stereoscopic image, the axis of the normaldistribution curve, and a segment represented by μ±n×σ is included inthe safe range of disparity, where p represents the average of thedisparities in the stereoscopic image, σ represents the standarddeviation, and n is a positive number (or a natural number).

While the stereoscopic image output device according to the presentinvention has been described above with reference to the embodiment, thepresent invention is also applicable to a stereoscopic video formed of aplurality of stereoscopic images.

Specifically, the image acquisition unit 102 acquires a plurality ofleft-eye images and a plurality of right-eye images which form astereoscopic video in playback order of the stereoscopic video. Thestereoscopic image output device may serve as a stereoscopic videooutput device by performing the process described with reference to theembodiment on each of the left-eye images and the right-eye imagesincluded in the stereoscopic video.

In the stereoscopic image output device serving as the stereoscopicvideo output device, the notification unit 104 notifies a viewer thatthe stereoscopic video is not a safe video in a period where thestereoscopic image determined to be unsafe by the safety determinationunit 103 is included.

Here, the notification unit 104 included in the stereoscopic imageoutput device serving as the stereoscopic video output device may notifythat the stereoscopic video is not a safe video once stereoscopic imagesdetermined to be unsafe by the safety determination unit 103 continuefor a fixed time period.

Alternatively, the output unit included in the stereoscopic image outputdevice serving as the stereoscopic video output device may stop outputof the stereoscopic video in a period in which the stereoscopic imagesdetermined to be unsafe by the safety determination unit 103 areincluded.

It should be noted that while the present invention has been describedwith reference to the above embodiment, the present invention is, ofcourse, not limited to the above embodiment. The present inventionincludes the following variations.

(1) The devices described above can be implemented in, specifically, acomputer system which includes a microprocessor, a ROM, a RAM, a harddisk unit, a display unit, a keyboard, a mouse, and the like. A computerprogram is stored in the RAM or the hard disc unit. By themicroprocessor operating in accordance with the computer program, eachdevice achieves its function. Here, the computer program is, to achievepredetermined functionality, configured in combination with a pluralityof instruction code indicating instructions to the computer.

(2) Part or the whole of the components included in each of the devicesdescribed above may be configured with one system LSI (Large ScaleIntegration). The system LSI is a super multi-function LSI manufacturedby integrating a plurality of components on one chip, and is,specifically, a computer system which includes a microprocessor, a ROM,a RAM, and the like. A computer program is stored in the ROM. The systemLSI achieves its function by the microprocessor loading the computerprogram from the ROM into the RAM and performing operations such ascomputing in accordance with the loaded computer program.

(3) Part or the whole of the components included in each of the devicesdescribed above may be configured with an IC card or a single moduleremovably attached to each device. The IC card or the module is acomputer system which includes a microprocessor, a ROM, a RAM, and thelike. The IC card or the module may include the super multi-function LSIdescribed above. The IC card or the module achieves its function by themicroprocessor operating in accordance with the computer program. The ICcard or the module may be of tamper-resistant.

(4) The present invention may be implemented in the methods describedabove. Moreover, the present invention may be achieved in a computerprogram implementing the methods by a computer, or may be achieved indigital signals which include the computer program.

Alternatively, the present invention may be implemented in acomputer-readable recording medium having stored therein a computerprogram or digital signals, for example, a flexible disk, a hard disk,CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray Disc), or a semiconductormemory. Alternatively, the present invention may be implemented in thedigital signal stored in these recording media.

The present invention may transmit the computer program or the digitalsignals via an electric communication line, a wireless or wiredcommunication line, a network represented by the Internet, databroadcast, or the like.

Moreover, the present invention may be implemented in a computer systemwhich includes a microprocessor and a memory, the memory may storetherein the computer program, and the microprocessor may operate inaccordance with the computer program.

Moreover, by transferring the program or the digital signals stored inthe recording medium, or transferring the program or the digital signalsvia the network or the like, the program or the digital signals may beexecuted in other independent computer system.

(5) The above-described embodiment and variations may be combined.

The embodiment and the variations of the stereoscopic image outputdevice according to one aspect of the present invention have beendescribed.

The stereoscopic image output device according to the embodiment canaccurately determine the safety of the stereoscopic image and thestereoscopic video when displaying the stereoscopic image and thestereoscopic video, and notify the user of the determination result.

This notifies the viewer that a stereoscopic image and a stereoscopicvideo are unsafe when the stereoscopic image and the stereoscopic videohave great disparities. Thus, the adversely effect to the viewer'shealth can be prevented.

Moreover, the stereoscopic image output device according to eachembodiment described above is implemented in, for example, a DSC shownin (a) of FIG. 12 or a digital video camera shown in (b) of FIG. 12.

Moreover, for example, the stereoscopic image output device according tothe above embodiment is implemented in a TV 700 shown in FIG. 13. Here,specific configuration of the display unit 106 is, although notparticularly limited to, a liquid crystal display, a plasma display, oran organic EL display which can perform stereoscopic display, forexample. In this case, the image acquisition unit 102 acquires imagesfrom television broadcasting, a Blu-Ray player 710 and a set top box 720shown in FIG. 13.

Moreover, the stereoscopic image output device may be implemented in theBlu-Ray player 710. In this case, the image acquisition unit 102acquires images from a Blu-Ray disc inserted into the Blu-Ray player710. The images may be acquired, not limited to from the Blu-Ray disc,from any recording medium such as a DVD and a hard disc drive (HDD).

Furthermore, the stereoscopic image output device may be implemented inthe set top box 720. In this case, the image acquisition unit 102acquires images from cable television broadcasting and the like.

The present invention can also be implemented in a stereoscopic imageoutput method.

The present invention is not limited to the embodiment and thevariations thereof. Various modifications to the present embodiment orthe variations thereof that may be conceived by those skilled in the artor other embodiments constructed by combining constituent elements indifferent embodiment or the variations thereof are included in the scopeof the present disclosure, without departing from the essence of thepresent disclosure.

INDUSTRIAL APPLICABILITY

According to the present invention, the safety of the stereoscopic imageand the stereoscopic video can be accurately determined by obtaining thenormal distribution curve of disparities in the stereoscopic image.Thus, the present invention is useful as a stereoscopic image outputdevice for use in digital TVs and digital cameras.

REFERENCE SIGNS LIST

-   100 Stereoscopic image output device-   101 Stereoscopic image generation unit-   102 Image acquisition unit-   103 Safety determination unit-   104 Notification unit-   106 Display unit-   107 Input unit-   120 First image-   130 Second image-   140 a, 140 b, 140 c, 140 d, 140 e, 140 f Feature point-   140 a′, 140 b′, 140 c′, 140 d′, 140 e′, 140 f′ Feature point-   140 c″, 140 d″ Feature point-   150 a, 150 b, 150 a′, 150 b′ Brightness vector-   160 Left-eye image-   170 Right-eye image-   700 TV-   710 Blu-ray player-   720 Set top box

1. A stereoscopic image output device comprising: an image acquisitionunit configured to acquire a left-eye image and a right-eye image whichform a stereoscopic image; an output unit configured to output theleft-eye image and the right-eye image acquired by the image acquisitionunit; a safety determination unit configured to determine whether thestereoscopic image is a safe image by comparing a normal distributioncurve obtained from disparities between corresponding points in theleft-eye image and the right-eye image and a safe range of disparityindicating a range of disparity in which the stereoscopic image isrecognized as a safe image for a viewer; and a notification unitconfigured to notify the viewer that the stereoscopic image is not asafe image when the safety determination unit determines that thestereoscopic image is not a safe image.
 2. The stereoscopic image outputdevice according to claim 1, wherein the safety determination unit isconfigured to extract, from the left-eye image and the right-eye image,a plurality of feature points for specifying a shape of a subjectincluded in the stereoscopic image, calculate disparities between thefeature points corresponding to each other in the left-eye image and theright-eye image, and approximate a frequency distribution of thecalculated disparities, to calculate the normal distribution curve. 3.The stereoscopic image output device according to claim 1, wherein thesafety determination unit is configured to determine that thestereoscopic image is a safe image when a percentage of an area of aregion included in the safe range of disparity over an area of a regionenclosed by the normal distribution curve is greater than or equal to apredetermined threshold.
 4. The stereoscopic image output deviceaccording to claim 1, wherein the output unit is a display unitconfigured to alternately display the left-eye image and the right-eyeimage, and when the safety determination unit determines that thestereoscopic image is not a safe image, the notification unit isconfigured to show, on the display unit, that the stereoscopic image isnot a safe image.
 5. The stereoscopic image output device according toclaim 4, wherein the display unit is configured to alternately displaythe left-eye image and the right-eye image only when the safetydetermination unit determines that the stereoscopic image is a safeimage.
 6. The stereoscopic image output device according to claim 1,further comprising a stereoscopic image generation unit configured toacquire a first image and a second image obtained by taking images of asubject from different positions, and rotate or move the second image sothat disparities between corresponding points in the first image and thesecond image are minimized in a vertical direction of the first imageand the second image, to generate a third image, wherein the imageacquisition unit is configured to acquire one of the first image and thethird image as the left-eye image, and the other as the right-eye image.7. The stereoscopic image output device according to claim 1, whereinthe image acquisition unit is configured to acquire a plurality of theleft-eye images and a plurality of the right-eye images which form astereoscopic video in a playback order of the stereoscopic video.
 8. Thestereoscopic image output device according to claim 1, wherein the saferange of disparity is a range of disparity determined by a biomedicalsafety guideline.
 9. A stereoscopic image output method comprising: (a)acquiring a left-eye image and a right-eye image which form astereoscopic image; (b) outputting the left-eye image and the right-eyeimage acquired in step (a); (c) determining whether the stereoscopicimage is a safe image by comparing a normal distribution curve obtainedfrom disparities between corresponding points in the left-eye image andthe right-eye image and a safe range of disparity indicating a range ofdisparity in which the stereoscopic image is recognized as a safe imagefor a viewer; and (d) notifying the viewer that the stereoscopic imageis not a safe image when it is determined that the stereoscopic image isnot a safe image.